The effect of ablation pattern on LA-ICPMS analysis of otolith element composition in hake, Merluccius merluccius

Laser ablation ICPMS (inductively coupled plasma mass spectrometry) analysis is a powerful tool for studies of fish ecology, based on measurement of the chemical composition of otoliths (ear stones). A key trade-off for this analysis is selecting the size of the ablation area to maximize the resolution for discrete temporal intervals during the life of an individual fish, vs the amount of otolith material required to produce reliable data. Three different widths of ablation lines were used to analyze the otoliths of European hake (Merluccius merluccius). The best temporal resolution was produced by ablation lines of 10 μm width, corresponding to less than 2 weeks in the fish's life, but the data from this configuration were variable and often below the detection limit for many elements. Ablation lines of 20 and 30 μm width produced accurate and precise data corresponding to approximately 20 and 30 days in terms of temporal resolution. When tested on hake otoliths, the measured element concentrations differed significantly between the 20 and 30 μm lines. The 30 μm ablation line resulted in a better multivariate model for discrimination between populations, with higher classification success and higher probability of individual assignment to source location

Temporal genetic stability and high effective population size despite fisheries-induced life-history trait evolution in the North Sea sole

Heavy fishing and other anthropogenic influences can have profound impact on a species' resilience to harvesting. Besides the decrease in the census and effective population size, strong declines in mature adults and recruiting individuals may lead to almost irreversible genetic changes in life-history traits. Here, we investigated the evolution of genetic diversity and effective population size in the heavily exploited sole (Solea solea), through the analysis of historical DNA from a collection of 1379 sole otoliths dating back from 1957. Despite documented shifts in life-history traits, neutral genetic diversity inferred from 11 microsatellite markers showed a remarkable stability over a period of 50 years of heavy fishing. Using simulations and corrections for fisheries induced demographic variation, both single-sample estimates and temporal estimates of effective population size (Ne) were always higher than 1000, suggesting that despite the severe census size decrease over a 50-year period of harvesting, genetic drift is probably not strong enough to significantly decrease the neutral diversity of this species in the North Sea. However, the inferred ratio of effective population size to the census size (Ne/Nc) appears very small (10−5), suggesting that overall only a low proportion of adults contribute to the next generation. The high Ne level together with the low Ne/Nc ratio is probably caused by a combination of an equalized reproductive output of younger cohorts, a decrease in generation time and a large variance in reproductive success typical for marine species. Because strong evolutionary changes in age and size at first maturation have been observed for sole, changes in adaptive genetic variation should be further monitored to detect the evolutionary consequences of human-induced selection

Maintenance of genetic variation and panmixia in the commercially exploited western rock lobster (Panulirus cygnus)

Marine species with high fecundities and mortalities in the early life stages can have low effective population sizes, making them vulnerable to declines in genetic diversity when they are commercially harvested. Here, we compare levels of microsatellite and mitochondrial sequence variation in the western rock lobster (Panulirus cygnus) over a 14-year period to test whether genetic variation is being maintained. Panulirus cygnus is a strong candidate for loss of genetic variation because it is a highly fecund species that is likely to experience high variance in reproductive success due to an extended larval planktonic stage. It also supports one of the largest and most economically important fisheries in Australia, with landings of between 8,000 and 14,500 tons (~70 % of the total legal-sized biomass) being harvested in some years. We found remarkably high levels of genetic variation in all samples and no evidence of a decline in genetic diversity over the time interval we studied. Furthermore, there was no evidence of a recent genetic bottleneck, and effective population size estimates based on single sample and temporal methods were infinitely large. Analysis of molecular variance indicated no significant population structure along 960 km of coastline or genetic differentiation among temporal samples. Our results support the view that P. cygnus is a single, panmictic population, and suggest genetic drift is not strong enough to reduce neutral genetic diversity in this species if current management practices and breeding stock sizes are maintained

Misidentification of bluefin tuna larvae: a call for caution and taxonomic reform

The international effort to prevent the collapse of Atlantic bluefin tuna (BFT, Thunnus thynnus, Scombridae) stocks exemplifies the challenges associated with modern marine resource conservation. Rampant mismanagement, under-reporting and illegal, unreported and unregulated fishing led to decades of over-exploitation in the BFT fishery. Surveys of larval abundance in the Gulf of Mexico and the Mediterranean Sea have been used as a proxy for both spawning biomass and recruitment by researchers working to improve estimates of stock abundance. Recent genetic barcoding studies have revealed that species identification errors are common among larvae surveys that use morphology-based taxonomy alone. Misidentification of larvae can lead to uncertainty about the spatial distribution of a species, confusion over life history traits and population dynamics, and potentially disguise the collapse or recovery of localized spawning sites. In an effort to identify the source of these errors, we review several weaknesses in modern morphology-based taxonomy including demographic decline of expert taxonomists, flawed identification keys, reluctance of the taxonomic community to embrace advances in digital communications and a general scarcity of modern user-friendly materials. Recent advances in molecular techniques useful for specimen identification and population studies are discussed at length. We advocate a more constructive integration of morphology-based taxonomy and barcoding in order to add confidence to larval surveys and to strengthen associated fisheries managementVersión del editor2,270